1. Field of the Invention
The present invention relates to an intake silencer system including an intake duct which communicates at opposite ends thereof with the atmospheric air and an engine, respectively, and whose intermediate portion opens into an intake silencing chamber.
2. Description of the Prior Art
An intake silencer system is known, for example, from Japanese Patent Application Laid-Open No. 8-158965. As shown in FIG. 6, in the known intake silencer system, a first silencing chamber 02 and a second silencing chamber 03 are defined in a case 01 by division of the inside of the case 01. A first intake duct 04 communicating with an engine and a second intake duct 05 communicating the atmospheric air, are opposed to each other, within the first silencing chamber 02. The second intake duct 05 communicates with the second silencing chamber 03 through a communication pipe 06. In this manner, a silencing function is obtained by the resonance effect of the first and second silencing chambers 02 and 03.
The above known system suffers from the following problem: Each of the first and second silencing chambers 02 and 03 exhibits a silencing effect only in a single frequency band. For this reason, to ensure that the silencing effect is exhibited in a wider frequency range, it is necessary to further increase the number of the silencing chambers, or to add a side branch. This is complicated and increases the size of the structure of an intake silencer system, resulting in an increased cost. Another problem of the above known system is that the wall surface of the case 01 is formed from a simple flat surface and thus has a low rigidity and hence, the wall surface is vibrated to thereby increase the radiated sound.